This invention relates to fuel injection nozzles for use in fuel systems for supplying fuel to internal combustion engines, the systems incorporating a high pressure fuel supply means which is connected to a nozzle inlet by means of a high pressure pipeline, the fuel supply means being arranged to supply fuel to the nozzle inlet in timed relationship with an associated engine, the fuel injection nozzle being of the so called inwardly opening type employing a spring loaded fuel pressure actuated valve member which is movable by fuel pressure away from a seating to allow fuel to flow from the nozzle inlet through an outlet.
Such systems and fuel injection nozzles are well known in the art. In an example the high pressure fuel supply means is a cam actuated plunger pump in which fuel delivery takes place when the plunger is under the control of the leading flank of the cam at a time depending upon the amount of fuel previously supplied to the pumping chamber of the pump. The flow of fuel to the injection nozzle ceases when the plunger inward movement ceases as an associated cam follower moves over the crest of the cam lobe. The initial outward movement of the plunger which then takes place, causes a reduction in pressure in the pipeline and this facilitates closure of the valve member of the fuel injection nozzle. The rate of pressure reduction at the nozzle is relatively slow.
Systems employing a cam actuated pumping plunger are known in which the supply of fuel to the fuel injection nozzle is halted by opening a spill valve before the inward movement of the plunger is complete. The spill valve may be an electromagnetically operated valve and such an arrangement can provide for more rapid closure of the valve member of the fuel injection nozzle, a factor which is important from the point of view of minimising engine exhaust emissions. The exhaust emission regulations are becoming progressively tighter and as a result there is a tendency for the fuel injection pressures to be increased coupled with a demand for more rapid closure of the valve member of the fuel injection nozzle. The rate of the reduction of pressure at the inlet of the fuel injection nozzle is very much dependent upon the inertia of the fuel and the characteristics of the pipeline which connect the fuel supply means to the nozzle and also if such are provided, outlet valves in the outlet of the fuel pump.